The Synthesis Of Nanoscale Zero-valent Iron Composite And Its Application In Wastewater Treatment

Heavy metal ion and floating oil have brought great harm to ecological environment and personal safety. Nanoscale zero-valent iron?NZVI? has attracted great attention in the field of wastewater treatment due to its rich raw materials, simple preparation, high activity, strong reducing potential, magnetic recovery property and environmental friendliness. However, NZVI is easy to aggregate and be oxidized, which limit its practical application in the wastewater treatment. To overcome these defects, magnetic NZVI composites with high dispersity, stability and activity were synthesized by inorganic/organic modified method. The as-synthesized composites were used to remove Cr??? and motor oil in aqueous solution. The contents were summarized as follows:?1? SiO₂-modified NZVI composite?S-NZVI? was synthesized by combining liquid phase reduction method with improved St?ber method. The influence of the molar ratio of SiO₂/Fe?ns/ni? on the morphology, structure and Cr??? removal efficiency of S-NZVI was investigated. The results indicated that S-NZVI exhibited spherical nanoparticles and distinguished core/shell structure. S-NZVI has high dispersity, small particle size and relatively uniform size distribution at ns/ni=1. The average particle size of S-NZVI was measured to be 53 nm. The Cr??? removal efficiency of S-NZVI reached 97 % at an initial Cr??? concentration of 80 mg/L.?2? Siloxane-modified NZVI composite?HS-NZVI? was synthesized via modifying S-NZVI?ns/ni=1? with siloxane, and used for Cr??? removal from aqueous solution. The Cr??? removal efficiencies were systematically investigated as a function of contact time, initial solution p H and Cr??? concentration. It was found that HS-NZVI exhibited spherical nanoparticles, high dispersity and distinguished core/shell structure. The average particle size of HS-NZVI was measured to be 59 nm. HS-NZVI possessed high BET surface area?65.9 m2/g? and large saturation magnetization?75.1 emu/g?. The maximum Cr??? removal capacity of HS-NZVI reached 292.8 mg Cr/g Fe, and removal data were well described by the pseudo-first-order reaction model. The Cr??? removal efficiency of HS-NZVI increased markedly with decreasing solution p H, and the maximum removal efficiency was 97.2 % at p H=3. Moreover, HS-NZVI exhibited higher stability and reusability in solution than pure NZVI and S-NZVI. SEM-EDX, XRD and XPS analyses of the products after reaction revealed the mechanism of Cr??? removal by HS-NZVI was mainly involved in adsorption, reduction and co-precipitation.?3? Hydrophobic composites?M-NZVI, O-NZVI and H-NZVI? were synthesized by modifying S-NZVI?ns/ni=1? with different chain length?C1, C8 and C16? of hydrophobic material, respectively. The influence of organic chain length on the contact angle, stability, oil adsorption capacity and magnetic property of as-synthesized composites was investigated in detail. As organic chain length increased, the contact angle, stability and oil adsorption capacity of as-synthesized composites increased markedly, but magnetic property decreased slightly. Among them, H-NZVI exhibited superhydrophobic and good magnetic recovery property, and the contact angle and saturation magnetization were 151.2 ° and 54.9 emu/g, respectively. Moreover, H-NZVI possessed high stability, which was hardly oxidized in Na Cl solution for 32 d. The maximum adsorption capacity of H-NZVI for motor oil was about 9.73 g/g, which was higher than those of M-NZVI?6.11 g/g? and O-NZVI?7.86 g/g?. The adsorption capacity?9.43-9.73 g/g? and contact angle?139.9-150.1 °? of H-NZVI after adsorption changed little in the p H range of 3-12, which showed H-NZVI could be applied in a wide range of p H. The adsorption capacity of H-NZVI still reached 9.26 g/g in the seventh cycle, indicating that H-NZVI had excellent reusability and stablilty.